1. Field of the Invention
This invention relates to devices enabling the transmission, as an output, of a translational motion only while the input motion can be considered as a double motion of both translation and of rotation and relates, more particularly to devices enabling the transmission to a sensor of an instruction relating to the displacement in translation of a movable member with the exception of possible rotational movements of the movable member which are to be transmitted to the sensor as a measurement of the displacement in translation.
2. Description of the Prior Art
This problem may be encountered in numerous control systems but the invention has a particular relationship to the case where the movable member at the input of the device is a cylindrical sleeve displaced by a fluid and subject to no guidance in translation motions, which may cause it to be subjected to rotational motion, while the output device is constituted by two mutually parallel rods which are movable in translation in fixed supports disposed at the outside of the sleeve and for these reasons the rods are not required to undergo any rotation whatsoever during their translational motion.
The invention can be applied to fuel dispensing pistons in engine fuel control units, for example for turbo machines. Within this sphere of activity, devices of the preceding generation were wholly hydraulic and the problem now encountered did not arise. Since then, the tendency of engine manufacturers has been to make the devices electro-hydraulic, the control as such being wholly electronic and an electro-hydraulic interface enables either the control of the hydraulic parts, or of the transmission of electrical signals derived from hydraulic elements. Amongst the signals which may be encountered are pressure signals, flow signals displacement signals, etc. . . . and the invention here described, concerns a fuel dispensing piston, the variation in the linear location of the piston enabling knowledge at any given instant of the quantity of fuel being delivered to the engine fuel injectors.
The present day tendency for the manufacturer of control units is to make the electronic part of the control predominant and extends to giving complete authority to the electronic control computers. So that the viability of the latter cannot be subject to default, coupling systems are provided such that during operation there is a degree of redundancy. Similarly, measurements are effected in parallel so that even if the sensors were non-usable for any reason whatsoever, the required signal will nevertheless be transmitted to the computer by the other sensor.
Such a device is described in U.S. Pat. No. 3,688,495 where the displacement of a pointer is measured by a soft iron core controlled by two induction windings disposed in an extension of the one from the other and actuated either alternatively or simultaneously in a differential manner.
This type of device has the disadvantage of requiring substantial axial space.
Other types of twin detectors are also known in which a detectoor is located at one side of a slide valve of which the displacement is measured and the other detector on the opposite side of the slide valve, which, however, gives rise to the same disadvantage of substantial space usage.